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Production of ethanol, a federally subsidized home-grown gasoline additive, is rising fast across the country.

But flooding the country with a corn-based biofuel has its unforeseen downsides. Among them is the huge water consumption required by ethanol plants.

Tampa officials discovered this recently when they received a request for 400, 000 gallons of water a day from U.S. EnviroFuels, a company seeking to build an ethanol plant in the Port of Tampa. Consumption could rise to 800, 000 gallons under the company's expansion plans.

The request, which would make the plant one of the city's top 10 water users, comes at a time when a short supply of water has forced once-a-week lawn watering restrictions on Tampa residents for more than a year, water bills are rising and the city is under pressure to allow more fresh water to flow into the Hillsborough River, the city's main water supply source.

"It would be a significant water burden, " Steve Daignault, the city's director of public works and utilities, said of the plant. "We have reached the top limit of our water use permit and we're at the point where we're having to buy more and more water."

77 plants in works

Water usage is one of the biggest hurdles facing the ethanol industry, second only perhaps to concerns over a rise in some food prices due to increased demand for corn. One recent report by the Minneapolis-based Institute for Agriculture and Trade Policy, described water as the "Achilles' heel" of corn-based ethanol.

There are 120 ethanol plants in the United States with another 77 under construction, mostly in the Midwest. The U.S. EnviroFuels project is the first in Florida. Several other ethanol projects are under way in Florida, but are still only in the planning stages.

By the end of 2008, the demand from new ethanol plants would require a 254 percent increase in the volume of water used by the industry over the previous decade, the IATP report estimated. It is also noted that "minimal data" exists on the impact to underground water aquifers.

To reduce the demand on local drinking water, the city of Tampa is working with U.S. Envirofuels on a plan to provide the plant with treated wastewater, which would otherwise be dumped into the sea.

"Once we are served with reclaimed waste water from the city, we can reduce our potable water requirement minimally by 65 percent, " said Bradley Krohn, president of U.S. EnviroFuels.

Advantages over costs

Although reclaimed water is cheaper per gallon than potable water, it will cost $3-million to $5-million to build a 2.5-mile pipe from the city's wastewater treatment plant to the port , and add about $1.1-million to the cost of building the ethanol plant.

But those costs were outweighed by the advantages of using reclaimed water to minimize the impact on the aquifer, said Krohn.

The city of Tampa dumps more than 50-million gallons of reclaimed water every day into Tampa Bay and wants to find industrial uses for it.

Using reclaimed water would make Krohn's plant stand out in an industry concentrated mostly in the rural Midwest, where plants pump directly from underground aquifers.

"Eventually, the industry's going to have to do better at promoting the use of reclaimed water, " Krohn said. "We will be a leader in that arena."

Improving efficiency

Engineering firms are exploring other ways to improve the efficiency of water use in ethanol plants.

A modern ethanol plant uses about 3 gallons of water to produce 1 gallon of ethanol, said Paul Greene, a senior director for biofuels with Siemens Water Technologies, designers of the water purification technology used in ethanol plants. That was an improvement on 4 gallons a year ago, but current technology is unlikely to improve much beyond that.

"There are things you can close loop and things you can't, " he said, referring to methods used to recapture water before it exits the plant, either as steam or dirty waste water.

Some industry experts think technology could reduce the ratio to 1.5:1 or even to 0 by recapturing steam lost to the atmosphere, as well as using moisture in the corn.

Biofuels advocates point out that the water use in an ethanol plant is no different than many other similar industrial processes, such as distilleries, refineries and even chip-rinsing in the micro-electronics industry.

However, gasoline compares favorably to ethanol with only about half a gallon of water required per gallon of gasoline, according to industry experts.

Unlike ethanol, gasoline does not require water in the front-end "cooking" process, said Jorge Pinon, a former oil executive with Amoco, who supports using ethanol as a fuel additive. "Oil refineries only need water for the cooling tower, " he said.

Most of the water - about 60 percent - is used in the cooling tower, which is where the ethanol is converted from a super-hot vapor into liquid fuel. Another 20 percent is absorbed into the ethanol itself, while the remaining 20 percent is used to feed the boiler. The corn feedstock is boiled to separate the ethyl alcohol from the corn starch in a process similar to a brewery. An ethanol vapor is then sent to the cooling tower to convert it into liquid form. "That takes a lot of cooling. The water is used to suck up the heat, " says Paul Greene, an industry expert with Siemens, the engineering giant.

Other ethanol projects in Florida

- Fort Lauderdale-based Losonoco Inc. is renovating a shuttered ethanol plant in Mulberry. The small plant will have a capacity of 12-million gallons per year.

-Citrus Energy LLC, is planning to build a 4-million-gallon-per-year ethanol bio-refinery in Clewiston using citrus waste. The Boca Raton-based company estimates that there is enough Florida citrus waste to produce 80-million gallons of ethanol a year.

- Alico Inc., a large land management company based in La Belle, is jointly investigating a cellulosic ethanol project using cellulosic gasification technology developed by Bioengineering Resources Inc. of Fayetteville, Ark. The project won a $33-million grant from the Department of Energy this year.

- The University of Florida is building a small-scale demonstration plant at the university's Energy Research Park to develop its own patented biofuels technology.

- Florida International University and Florida Crystals Corp. in Okeelanta are collaborating on a study to convert sugar cane bagasse to ethanol.